1. Field of the Invention
This invention relates to a spatial light modulation device (hereunder sometimes referred to simply as a spatial light modulator) to be employed as an optical computing element (or arithmetic device) for use in an optical computer or for optical information processing, or employed as a display element for use in a projection display.
2. Description of the Related Art
Hereinafter, a conventional spatial light modulator employing a semiconductor single crystal will be described by referring to FIG. 3. As shown in this figure, a side surface of a high-resistance (or high-resistivity) N-type silicon 2, which is a photoconductor layer, is bonded onto a transparent insulating substrate 1 through an N-type low-resistance layer 3 in this spatial light modulator. Further, a plurality of Schottky electrodes 4 are formed on the other side surface of the high-resistance N-type silicon 2. Each of the Schottky electrodes 4 is separated by insulating films 5 from the others of the Schottky electrodes 4 and forms a pixel electrode. Moreover, a dielectric mirror layer 6 is formed on the Schottky electrodes 4. Furthermore, a transparent electrode 8 and a liquid crystal layer 9 which is employed as a light modulator (or an optical modulator) are held between this dielectric mirror layer 6 and a transparent insulating substrate 7. Incidentally, reference numeral 10 designates spacers which are inserted between the dielectric mirror layer 6 and the transparent electrode 8 and are used to establish a predetermined thickness of the liquid crystal layer 9.
Next, an operation of this conventional spatial light modulator will be described hereinbelow. First, a square-wave voltage is applied from a driving power source 11 across the low-resistance layer 3 and the transparent electrode 8. Then, if a negative voltage is applied to the transparent electrode 8, the Schottky junction is biased in the reverse direction and a depletion layer is extended or enlarged. Further, write light FA, which is incident on the depletion layer from the transparent substrate 1, generates electron-hole pairs. Then, the positive holes are moved to the Schottky electrode 4 through the depletion layer in the presence of an electric field and are further stored in the electrode 4. This results in increase in voltage applied to the liquid crystal layer 9.
Subsequently, when a positive voltage is applied to the transparent electrode 8, the Schottky junction is biased in the forward direction and all of positive charges stored in the electrodes 4 are emitted therefrom. Further, all of the driving voltage is applied to the liquid crystal layer 9.
Thus, a negative voltage to be applied to the transparent electrode 8 is so set that the voltage applied to the liquid crystal layer 9 in a dark state is equal to or less than a driving threshold voltage. On the other hand, a positive voltage is applied to the transparent electrode 8 for a short period of time sufficient to such an extent that the liquid crystal layer 9 does not operate. Thereby, in a portion of the layer 9, on which the write light FA is incident, the direction of polarization of reflection light FC, which is obtained by reflecting read light FB, is modulated due to birefringence (namely, double refraction) thereof occurring in the liquid crystal. Consequently, the modulation of read light corresponding to written information can be realized.
However, the sensibility (or sensitivity) of the conventional monocrystalline spatial light modulator is dependent on the quantum efficiency obtained in the depletion layer. Further, in case of simple Schottky junction, P-N structure or junction, or P-I-N junction, the quantum efficiency can not be more than 1. Thus, the sensibility of the conventional monocrystalline spatial light modulator has its limit.
The present invention is created to eliminate the above described drawback of the conventional spatial light modulator.
It is, therefore, an object of the present invention to provide a spatial light modulator which has high sensibility.